An automatic analyzer for clinical tests dispenses predetermined amounts of a reagent and a sample for subsequent mixing and reaction. Absorbance of a reaction solution is then measured for a predetermined period of time and, based on measurements, concentration and activity values of substances to be measured are found.
Analyses for clinical tests require, in addition to an analyzer, a reagent for each analysis item, a standard solution for reagent calibration, an apparatus currently making an analysis, and a quality control sample to be measured for reagent status check. Combination of all these items but the analyzer achieves final analytical performance.
Internal factors of the analyzer directly affecting the analytical performance include, but are not limited to, a sampling mechanism, a reagent dispensing mechanism, a mixing mechanism, an optical system, a reaction vessel, and a thermostat. Factors other than an apparatus such as the automatic analyzer include a reagent, a sample, and liquidity of a control specimen.
In a case where the automatic analyzer is to be used on a daily basis, the foregoing factors need to be checked to thereby determine whether a normal clinical test can be made. Factors may, for example, be checked as follows.
(1) Calibration Using a Standard Solution
A reagent bottle for each item is calibrated. A blank solution and a standard solution are measured to thereby determine an origin and calculate absorbance per unit concentration and a conversion factor (hereinafter referred to as a K factor). In general, a clinical laboratory technologist determines the magnitude of absorbance and time-dependent variations in the K factor to determine whether the results of calibration are acceptable.
(2) Quality Control
A quality control sample with a known concentration is measured after the calibration to check for any difference from a reference value. If a patient specimen is being measured, the quality control sample is measured regularly at predetermined time intervals to thereby check for any deviation from a permissible value. If the permissible value is exceeded, an inspection is made on the assumption that something is wrong with either the reagent or analyzer.
In daily tests, data is checked using reaction process data. The prozone check is known for detecting abnormality in data in measurement in an endpoint method. With reagents used in the immunoturbidimetric method for measuring IgA (immunoglobulin A), CRP (C-reactive protein) and the like, protein may deposit as a precipitate as affected by salt concentration of reagent compositions. The precipitate may subject the reaction process to fluctuations that very often occur actually in a latter part of a reaction time. The fluctuations occurring at a photometric point used for calculation of concentration hampers accurate measurement. An antigen re-addition method and a reaction rate ratio method are available as methods for checking this. In either method, an alarm is issued to notify that a limit value specified with a parameter is exceeded.
Methods as disclosed, for example, in patent documents 1 and 2 are known as methods for determining whether there is an abnormality by using the reaction process data (time-series data of absorbance). In the method of patent document 1, reference time-series data is generated in advance using a chemical reaction model and stored in memory; reaction process data of the sample is then compared with the reference time-series data; the method determines that there is an abnormality when there is large deviation. The method of patent document 2 approximates a change in absorbance by using a function previously stored in memory and determines an abnormality based on the magnitude of deviation of actually measured absorbance from the absorbance calculated, in which the absorbance change thereof is approximated with the function.